http://modelEAU.fsg.ulaval.ca

alain.provist@gci.ulaval.ca

Turning a primary clarifier into a

fermenter: Analysis using titrimetry

Efficient Denitrification

Needs adequate COD source

Creates alkalinity

to maintain optimum pH

Objective:

Primary clarifier Fermenter

TAKE HOME MESSAGE

Titrimetry allows analyzing the pH and alkalinity profiles in a primary clarifier to monitor

the reactive settler’s performance and evaluate the VFAs produced in the sludge blanket.

It allows assessing the benefits for improved denitrification in the subsequent bioreactors.

How to turn a primary clarifier into a fermenter?

Titrimetry, a titration based method to measure VFAs

Buffer capacity curves: An application of titrimetry

Maryam Tohidi1,4, Michele Ponzelli2, Christophe Boisvert1, Elsayed Elbeshbishy2, Domenico Santoro3 and Peter A. Vanrolleghem1,4

1 modelEAU, Département de génie civil et de génie des eaux, Université Laval, 1605 Avenue de la Médecine, Québec (QC) G1V 0A6, Canada2 Ryerson University, Department of Civil Engineering, 350 Victoria Street, Toronto (ON) M5B 2K3

3 Trojan Technologies, 3020 Gore Road, London (ON) N5V 4T74 CentrEau, Université Laval, 1065 avenue de la Médecine, Québec (QC), G1V 0A6, Canada

Back valve

(automatic)

Back valve

(manual)

Pump

QIN

QE

QR

QW

XR

XR

TSSIN

TSSE

SAMPLING POINT

Figure 3. Schematic of the primary clarifier with recirculation

Computer Sample Processor Titrator

Data transfer

Data records

Soluble organic matter in the

form of VFAs by a higher degree

of fermentation in the primary

sludge blanket.

Nutrient removal rate in the

downstream treatment plant.

maryam.tohidi.1@ulaval.ca

Operational factors for VFA enhancement

- Increase sludge age in blanket

- Recirculation line from bottom back to inlet

- pH conditioning by dosing alkaline

Figure 1. pilEAUte plant bioreactor (anoxic zone in red)

Figure 2. pilEAUte plant primary clarifier

Figure 4. Internal recirculation set-up

0 200 400 600 800 1000

0,00

0,50

1,00

1,50

2,00

2,50

0 1 2 3 4 5 6 7 8

VFA (mg/L as CH3COO), Alkalinity (mg/L as HCO3)

Slu

dge

bla

nke

t h

eigh

t (m

)

pH

pH VFA AlkalinityFlow rates HRT SRT

QIN QR QW HRT SRT

m3/d %QIN m3/d h d

16.8 50% 0.04 2.1 1

Figure 6. Titration curve of a sludge blanket sample

Table 1. Operating and

environmental conditions

Figure 5. pH, VFA, and alkalinity profiles along the sludge blanket height

0,00

0,50

1,00

1,50

2,00

2,50

3,00

3,50

4,00

3,00 4,00 5,00 6,00 7,00 8,00

Buffer

Capacity (

meq/l/p

H)

pH

Experimental

Theoretical

Bicarbonate

VFA

H2O

Titrant = 0.01N H2SO4

3,0

3,5

4,0

4,5

5,0

5,5

6,0

6,5

7,0

7,5

8,0

0 20 40 60 80 100

pH

(-)

H2SO4 added (mL)

PHREEQC Simulation Experimental curve

What is my wastewater’s composition?

Simulating a down-titration with PHREEQC

Figure 7. Methrom Titrino device with a Sample Processor

Sample

Composition

Concentration

mg/L

pKa

1

pKa

2

Alkalinity (HCO3) 100.12 6.37 10.5

VFA (as CH3COOH) 442.72 4.76 -

Table 2. Calculated concentrations of VFAs

& Alkalinity based on the pKa values

Using a solver

Experimental curve ≅ Theoretical curve

(titration) (calculated)

Minimizing sum of

squared errors

Figure 8. Buffer Capacity Curve in meq/L/pH

Table 2. Calculated concentrations of VFAs &

Alkalinity using PHREEQC as a simulator

Figure 9. PHREEQC simulated curve fitted with

least error on the experimental curve

H2SO4 [0.01] N

Solution 1

Wastewater sample Solution 2

Wastewater sample

after titration

Running PHREEQC

Experimental curve ≅ PHREEQC curve

(titration) (calculated)

Running OpenSolver

Sample composition

• Reading database

• Simulating titration

Time-series

Minimizing sum of

squared errors by

running PHREEQC

for different iterations

Sample

Composition

Concentration

mg/L

Alkalinity (HCO3) 110.3

VFA (as CH3COOH) 446.32

3 ,5

4 ,0

4 ,5

5 ,0

5 ,5

6 ,0

6 ,5

7 ,0

7 ,5

0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0

** ** ** **

pH

V [m l]

pH

Volume acid added (mL)